Laptop computers are becoming increasingly popular for use by people who must travel or work in locations where desktop computers are not available or practical. Today's laptops are often just as powerful and feature-rich as many desktops. For example, many laptops now come equipped with large displays and full size keyboards. Although laptop computers are quite useful in appropriate situations, they are often either too large and/or too heavy to be used in remote locations, or where space is limited. Furthermore, battery life in laptop computers is typically only about 2-4 hours, further limiting their usefulness in remote locations. Finally, laptop computers may simply be overkill in situations where data entry is all that is required.
One alternative to the laptop computer for mobile data entry is the personal digital assistant (PDA). Unlike laptops, which use a computer keyboard for data entry, PDAs typically employ a stylus that is used to write on the screen of the PDA. The writing is then captured and processed using handwriting recognition software in the PDA. Unfortunately, the screens on most PDAs are relatively small, thus limiting the amount of text or data that can be entered and viewed at once. Furthermore, many PDAs require a user to learn and employ a special alphabet when inputting handwritten text.
A recent alternative to both the laptop and the PDA for mobile data entry is what is referred to as a pen based text entry system, or a digital pen. Digital pens typically allow users to write or draw on a pad of paper, and capture that writing or drawing to memory within the pen, or in an attached device, such as a PDA. The writing or drawing can then be transferred at a later time to a conventional computer for processing, such as handwriting recognition.
There are a number of ways in which digital pens capture text or writing. One such way involves the use of a tiny camera located within the pen to capture text or data as it is being written. These “camera based” pens require the use of special paper, which has a series of microscopic dots spaced throughout the paper. As a user writes on the paper with the pen, a tiny camera near the tip of the pen captures images of the dot pattern. A processor in the pen then uses the captured images to mathematically determine where the point of the pen was on the page at the moment the images were captured. By examining the changing dot patterns from image to image, the pen creates a virtual trail of where the pen tip has been. From this data, a record can be made of the path the pen has taken across the paper.
Unfortunately, these “camera based” digital pens have a number of drawbacks. The most significant of these drawbacks is the fact that special “dotted” paper must be used for the pen to function. This special paper is more expensive than standard paper. Additionally, this special paper is often not readily available. As such, to practically use a camera based digital pen, this special paper must be carried with you at all times.
One alternative to these camera based digital pens is an ultrasonic type digital pen. Current ultrasonic type digital pens employ a single ultrasonic transmitter in the pen that transmits an ultrasonic signal to an ultrasonic receiver unit, which is typically clipped or attached to a pad of paper. The ultrasonic receiver unit typically includes two ultrasonic receivers for receiving the signal transmitted from the pen. Using simple 2-dimensional triangulation techniques, the location of the tip of the pen on a 2-dimensional plane, such as a sheet of paper, can be determined.
Unfortunately, these ultrasonic type digital pens are not very accurate in determining the precise location of the pen tip during writing and drawing. The primary reason for this lack of accuracy relates to the position of the ultrasonic transmitter in the pen. Due to the size of the ultrasonic transmitter and the dimensions of the pen, the ultrasonic transmitter must be located some distance from the pen tip. This is not a problem when the pen is held in a perfectly perpendicular orientation relative to the paper. Held in this manner, the transmitter is aligned directly over the pen tip and, thus, in the same location in the 2-dimensional plane as the pen tip. However, when the pen is tilted the transmitter will no longer be aligned directly over the pen tip. Rather, the transmitter will be located some distance away from the pen tip in the 2-dimensional space. Since the receiver records the position of the transmitter, rather than the location of the pen tip, an inaccurate tip location will be recorded whenever the pen is tilted, which occurs naturally during writing.
Accordingly, there is a need for pen-based, mobile data capture system that accurately records the position of the tip of the pen, rather than the location of the transmitter and that does not require the use of special paper.